This invention relates generally to devices and methods for trapping blood clots and controlling embolization and thrombosis in blood vessels. More particularly, this invention relates to an apparatus and a method for providing protection from emboli and thrombi and for preventing occlusion in a blood vessel using a unique new trap for capturing emboli passing through the vessel. The trap includes an obturated below stem which maintains the trap in its desired location for as long as required, allows for the introduction of fluids to the region of the trap for purposes of venography and lysis of trapped emboli or thrombi, and permits the trap to be withdrawn when medically appropriate without releasing emboli or newly formed thrombi into the bloodstream.
The presence of emboli within the body's circulatory system presents significant health hazards from potential acute venous thrombosis and chronic deep vein thrombosis. Acute venous thrombosis can lead to pulmonary embolism, when an embolus travels into the plumonary arteries.
Surgical approaches to control both chronic deep vein thrombosis and acute venous thrombosis have been used for many years. Currently, the most widespread approach is treatment with systemic and oral anticoagulants, such as heparin and coumadin and with thrombolytic agents such as TPA, urokinase and streptokinase. The initial treatment of pulmonary embolism is similar.
Unfortunately, such chemical therapy is ineffective or inappropriate in some patients. Since most pulmonary emboli originate in veins of the lower limbs, pelvis or inferior vena cava, life-threatening pulmonary emboli can be prevented from reaching the lungs by mechanically interrupting the inferior vena cava to trap emboli, preferably proximally to the heart.
Indications for creating or introducing traps in the inferior vena cava include:
a) Pulmonary embolism in patients with a high risk of internal bleeding, including those having recent trauma, surgery, cerebral hemorrhage or peptic ulcer disease who are not amenable to anticoagulant or thrombolytic therapy. PA1 b) Recurrent pulmonary emboli notwithstanding anticoagulant therapy. PA1 c) Patients showing large free-floating thrombi in the iliofemoral veins or inferior vena cava identified with venography. PA1 d) As prophylaxis against pulmonary emboli in older patients with high-risk conditions. PA1 e) Disseminated thrombosis and profound thrombocytopenia in patients displaying heparin sensitivity. PA1 f) Prevention of recurrent pulmonary emboli after pulmonary thrombolectomy.
Techniques for mechanical interruption of the vena cava have included suturing grids across the inferior vena cava and applying external clips to the vessel to produce parallel, reduced orifices. Unfortunately, these procedures require general anesthesia and laparotomy subjecting patients who are already seriously ill to increased danger of post-operative complications and further may cause occlusion of the vena cava with all of its associated sequelae.
In 1967-68, Eichelter and Schenk described an umbrella-like device which they introduced under local anesthesia into the femoral vein of dogs to filter emboli. Eichelter, P., Schenk, W. G., Jr.: "A New Experimental Approach to Prophylaxis of Pulmonary Embolism", Rev Surg 24:455-456 (Nov-Dec) 1967; Eichelter, P., Schenk, W. G., Jr.: "Prophylaxis of Pulmonary Embolism", Arch Surg 97: 348-356 August 1968. The Eichelter/Schenk device was constructed by making longitudinal incisions circumferentially around a segment of a polyethylene tube, placing a tube of smaller diameter inside the larger tube and flaring the end protruding beyond the linear incisions. Light traction of the inner tube while holding the outer tube stable produced an umbrella-like structure. Unfortunately, this structure included numerous apertures for trapping stagnant blood and thereby promoting highly undesirable thrombosis and potential embolization.
Eichelter/Schenk made a small incision in the right femoral vein of the groins of the dogs used in the tests, with the distal portion of the catheter tied into the femoral vein and the device open at a point lying distal to the renal veins. After a number of weeks, the device was collapsed and removed through a small incision. The embolization of trapped or attached emboli upon removal of the Eichelter/Schenk device precluded use of this device in humans. No further study of application of this device has been reported, as far as the present inventors can ascertain.
A permanent implantable vena cava filter was developed by Mobin-Uddin in 1969, and described in U.S. Pat. No. 3,540,431. This filter is intended to be introduced through an incision in the jugular vein. The Mobin-Uddin filter is an umbrella-like structure having expanding ribs carrying sharpened points at their divergent ends which impale the walls of the blood vessel when the filter is positioned at the desired location and permitted to expand into its operative structure. The Mobin-Uddin filter has a high occlusion rate and is therefore not widely used. Furthermore, the sharpened points create the possibility of retroperitoneal bleeding from perforations in the vessel wall. Indicated heparin treatment is typically withheld for 12 hours after insertion to minimize the danger of this complication. Finally, even if initially properly implanted, these filters can come loose and migrate to either ineffective or dangerous and life-threatening locations in the vascular system.
The development of the Mobin-Uddin device lead to the introduction of a series of other permanently implantable filters, including the currently most widely used vena cava filter, the Kimray-Greenfield filter, described in U.S. Pat. No. 3,952,747. This filter, depicted at 10 in FIG. 1, comprises a plurality of wire legs 12 extending in a generally conical array from a nose 14 having a port 16. While the Kimray-Greenfield filter is structurally different from the Mobin-Uddin device, it also includes sharpened hooks 18 to permanently anchor the filter by impaling the hooks in the blood vessel walls 20 giving rise to the associated danger of retroperitoneal bleeding. As in the case of the Mobin-Uddin device, the Kimray-Greenfield filter can come loose and migrate to either ineffective or dangerous and life-threatening locations in the vascular system. Additionally, port 14 can trap and hold blood, promoting undesirable thrombosis and potential embolization.
The Kimray-Greenfield filter is difficult to load before emplacement due to the interference of the hooks with each other when the filter is folded into the ejector used in the emplacement. It is also difficult to emplace since it is a "one-shot" system--once the filter is ejected and implanted it cannot be moved. The Kimray-Greenfield is subject to premature or inadvartent ejection during emplacement, resulting in permanent placement at an inappropriate location and often requiring the placement of an additional filter at the desired location.
Another of the vessel wall anchoring devices is the Amplatz filter, which is described in "Amplatz Retrievable Vena Cava Filter," Seminars In Interventional Radiology, Vol. 3, No. 3, September 1986, by M. D. Darcy, D. W. Hunter, G. B. Lund, and J. F. Cardella. This filter is spider shaped, with six prongs each having a central wire that impales the vena cava wall, again raising the specter of retroperitoneal bleeding from perforations in the vessel wall. Although this device is described as being "retrievable", retrieval is both difficult and problematic.
The Amplatz filter is designed to be withdrawn through the femoral vein by ensnaring a hook at the caudal end of the filter, a difficult and oftentimes unsuccessful procedure. Furthermore, and perhaps more importantly, retrieval must be performed within the first several weeks after emplacement since the hooks become increasingly entrapped in the vessel walls due to encroaching fibrosis, raising an unacceptable danger of damage to the vessel architecture on removal after several weeks in place.
There are a multitude of problems associated with current vena cava filters designed to be fixed in place by way of hooks which impale caval or other blood vessel walls. A thrombus at the implant site can prevent or complicate engagement of the hooks. Even if initially properly implanted, the filters sometimes come loose and migrate to either ineffective or dangerous and life-threatening locations in the vascular system. Perforation of the vessel wall by the filter hooks occurs, with the danger of damage to the vessel wall, providing new sites for emboli formation, and a danger of puncture, causing internal bleeding and clinical sequela. Some of the filters are particularly subject to occlusion. Many tilt after or during emplacement permitting large, dangerous emboli to escape the filter into the bloodstream. The emplacement procedure for most current filters is cumbersome and requires large diameter ejector devices which are difficult to maneuver through blood vessels particularly when variations in the vessel architecture are encountered.
Finally, once the thrombotic condition sought to be treated is resolved--typically in about six weeks to six months--it is desirable to remove the filter to open up complete flow through the vessel and remove at best an unwelcome foreign body. Since the present filters are for all intents and purposes fixed permanently in place, this is not presently possible. Thus, the propriety of the use of the current devices is questionable, particularly in younger patients whose life expectancy is substantially great and the clinical need for the filter may be short. A great number of patients require only temporary safety from pulmonary embolization and prophylactic heparin may be contraindicated or otherwise unsafe particularly where surgery is contemplated.
The present invention solves the problems inherent in the prior art devices and methods by providing a system in which a quick and safe, positive, temporary emplacement of a compliant, conformable emboli trap is accomplished without impaling blood vessel walls or causing any of the other problems associated with prior art devices.